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Gather round, children, and listen up: if you do not yet own a drill chart go get one. Many places give them away for free but even if you buy one its hard to spend more than $3 so there's no excuse for not having one. I have one on my shop wall as big as a movie poster and a small laminated one right here next to the computer which I will use to answer Kev's question.
With the chart you can see the size in decimal of every drill that exists so, for example, Kev could look at a 1/8 drill and see that is.125 in decimal, he wants a clearance size hole for his pins so lets look for something about 5 thou larger than that. We see that a #30 drill is .1285 so that's 3.5 thou over and thats good enough. If you insist on the full 5 thou over then we see that a 3.3mm drill is .1299 and that's 4.99 thou so there you go. If you get really rabid about a specialty size MSC will sell you a drill sized by HALF a thou in any size you want.
These charts also show drill sizes for tapping holes of any reasonable size we would need. Get one of these charts and learn to luv it! It's also a good idea to own a dial caliper, while we're on the subject of drill sizes. Not all of your pin stock is nominal (that means a 1/8 pin might actually be .128 if you measured it). If it isn't then your usual #30 won't give you clearance. So, you measure with the dial caliper and then get a drill that will clear whatever you measured. Get a standard dial caliper in either 4" or 6" capacity - just a simple mechanical one, no digital. These can be had for under $15, or $20 if you get a really nice one. I have a $150 Starrett and an $11 Chinese one and they both read the same on the small stuff we work with so there's no excuse for not having these tools.
3/32 .0938 #40 (loose fit) #41 (close fit)
5/32 .1562 #21
1/4 .2500 F (.2570) 6.5mm (.2559)
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